The assignee of the present invention manufactures and deploys spacecraft for, inter alia, communications and broadcast services from geosynchronous orbit. A substantial number of radio frequency (RF) filters are required in such spacecraft. For example, a satellite input multiplexor (IMUX) may utilize a number of microwave channel filters, each filter having the functionality of separating and isolating a specific respective signal or bandwidth frequency from a broadband uplink signal received by a spacecraft antenna.
IMUX channel filters are required to exhibit high selectivity and high Q. These filters may include a plurality of cylindrical cavities, each cavity including an internally disposed disk-like dielectric resonator (or “puck”) to improve filter Q relative to physical size and bandwidth. Such filters are described, for example in U.S. Pat. Nos. 6,297,715, 8,907,742, and 8,952,769 assigned to the assignee of the present invention, the disclosure of each which is hereby incorporated by reference into the present application for all purposes.
The filter may operate in dual mode (e.g., HE11 mode) and each cavity of the filter may be coupled to at least one adjacent cavity via a respective aperture (or “iris”) that enable the HE11 field to couple between the cavities. The iris may have a slot-like configuration with a large aspect ratio of length to width. The iris may be disposed in a central portion of a common wall separating two adjacent cavities. The iris should be optimally sized in order for the filter to meet specified requirements. The optimal dimensions are difficult to predict. Moreover, dimensional variations resulting from machining tolerances can significantly affect filter performance.
In the absence of the present teachings, fabrication and testing of multiple common walls, each including an iris, the irises each varying slightly in size, may be necessary to find an iris size that provides the best performance.